Radiofrequency amplifying system



March 15, 1927.

L. L. JONES RADIO FREQUENCY AIV'IPLIFYING SYSTEM Filed March 6. 1926.

INVENTOR L'esrer L. Jones ATTORNEYS Patented Mar. 15, 1927.

UNITED STATES 1,620,661 PATENT OFFICE.

LESTER L. JONES, or QBADELL, NEW JERSEY.

- RADIOFREQUENCY AMIELIFYING SYSTEM;

Application filed March 6,1926; Serial No. 92,761.

This invention relates to electron dis;

charge tube amplifier circuits, and more par ticularly' to an improvement in the art ofing transition between the overdamping of the tuned stage and the production of excessive oscillations therein which was incident to prior methods of cascading untuned onto tuned radio frequency stages, the system of my invention being so constructed and designed that the feedback reactions between F the untuned stage and the tuned stage are stabilized for the whole wave length range for which the system is built so that such feed-back reactions may be completely neutralized for the predetermined range of frequenc'ies through which the tuned stage is operative.

In the preferred. form of this cascade amplifying' system of my invention, a pair of electron discharge devices or tubes are coupled together in cascade by untuned or nontunable means, the natural frequency of which is predetermined so as to prevent the produ'ctionof any damping reaction in the inputcircuit of the first tube which made tunable over a predetermined frequency range,,this natural frequency being furthermore such as to tend to create only an oscillation-crea'ting feed-back reaction in said tunable input circuit throughout the whole wave length or frequency range for which' the system is built. By this means I am enabled to fix or stabilize the oscillations; so

that means may be employed for effectively neutralizing or balancing the same; and means are provided for compensating for or neutralizing suchprimary feed-back reactions To accomplish the desired results,

the untuned coupling means for the electron discharge tubes are given selected constants. or characteristics such that the natural fre quency of the untuned coupled circuits is greater than the highest frequency of the predetermined frequency range through Y which thetuned input circuit of the first tube is tunable; and by thus selecting the natural frequency of the ,untunedicoupled circuits, the system will tend to oscillate during all changes in tuning of the tuned inputcircuit in the absence of any feedback neutralizing means so that a definite control may-be introduced to neutralize the v feed-back reactions which are due to the coupling inductance and which take placefirst tube of the pair. For convenience bf description, I term such feed-back reactions as adjacent stage feed-back.

My present invention relates to improvements in the cascade amplifying systemreferred to whereby disturbing reactions due to what I term a distant stage feed-back are effectively eliminated. I have found thatin the operation of this amplifying. system-a" disturbing reaction may takev place 'on' the tunable input circuit due to the. tuning of a non-tunable stage of the system. Ijhave .from the output to the input circuits of'thev 0 circuit arranged posterior to the untuned or further found that this disturbance exists even though all the external space channelswhereby the reaction might occurfare closed;

and although this disturbing reaction is not ofgreat Ina as a secondary as distinguished-from a; pm; mary feed-back reaction and which mayinotin and of itself give rise to a-iiy 'self:sus-

tairted oscillations or severe overdamping, I find that in a cascaded system of a large "number of steps of amplification the reaction ma interfere with and at timesdestroy the desi ed stability and sharpness of tuning of one or" more of the tunable circuits and that such disturbance together with other unavoidable and perhaps more distant stage feed-backs, give rise to self-oscillation, detuning, loss of selectivity, or other undesirable damping eflects. i

A principal objectof my present invention therefore resides in the provision of gnitude and may be considered:

means for completely eliminating these" sec;

ondary disturbing reactions of one tunable circult upon a preceding tunable circu'itin the above-described system, such improved means rendering it possible to construct a thoroughly stable multi-stage cascaded amplifier of high sensitivity and-predetermined selectivity free from inter-stage tuning reactions or oscillations,

To the accomplishment of the foregoing and such other objects as will hereinafter apar, m invention consists in the elements and their relation one to the other, a here inafter particularlydescribed and sought to be defined in the claims; reference being had to the accompanying drawings which show a preferred embodiment of my invention, and in which:

Fig. 1 is a wiring diagrammatic view- .of a radio receiving system embodying my inradio frequency amplification, and

Fig. 2 is a wiring diagranmiatic view of a portion thereof showing a cou le or pair of electron discharge tubes casca ed in accordance with the principles of my invention.

Referring now more in detail to the drawings and having reference first to Fig. 2 thereof, I show the invention applied to a radio frequency system embodying a pair of radio frequency tubes or electron discharge devices designated respectively as 1 R. F. and ,2 R. F., each of said electron discharge devices being of the three-electrode type having a filament, grid and plate denoted respectively by f, g and p with an exponent corresponding to the position of the tube in the series. The filaments are controlled by filament circuits all connected to the battery A, said filament circuits being denoted by the reference character F with an exponent corresponding to the position of the tube in the series, each of the filament circuits prefcrablylincluding a rheostat or resistance r, 1"""forrcgulating the temperatures of the filament.

The cascaded electron discharge devices each include input and output circuits designated as i and o'respectively with an exponent also corresponding to the position of the tube in the series, the input circuit 71' of the first tube being tunable through a predetermined range of frequencies and comprising the, coupling inductance or secondary S of a transformer T and the variable or tuning condenser C; and the out- 7 put circuit 0 of the second tube also being in effect a tuned circuit and comprising the primary P of the transformer T the secondary S of which is physically in the next succeeding circuit, the said output circuit 0 being tunable through the predetermined frequency range for which the system is designed by means of the tuning condenser C It will thus'be seen that the input circuit of the first tube and the output circuit of the second tubeare both' tunable through a predetermined wave length range.

As heretofore stated, the system of my invention comprises the cascading of untuned and tuned radio frequency stages, and

to this end the electron discharge tubes by non-tunable means which in the present embodiment of the invention comprises a coupling inductance L common to the cou-' pled circuits which are the output circuit 0 of the first tube and the input circuit 2' of the second tube, the input circuit 71 also including a fixed condenser K in series with the coupling inductance L. I

For stabilizing the adjacent stage feedback reaction in the first radio frequency tube 1 RF. due to the coupling inductance I.4 ,.i3l-lB,llI1tl1Il8(l coupled circuits .0'z' are vention and showing six. cascaded fiages of":

Gon'structed so that the natural frequency thereof is greater than the highest frequency through which the input circuit 2" is tunable, and by selecting this characteristic of the untuned coupled circuits there is produced an oscillation-creating feed-back reaction throughout the whole wave length or frequency range for which the system isfbuilt, which feed-back reaction may be neutralized for the whole frequency range. To produce the desired characteristic, the coupling in ductance' L is of the order of 0.13, millihenry and the capacity of the condenser K may have a value of .0001 to .001 microfarad and upwards with tubes having grid platecapacity of ten microfarads and over a wave length band of 200 to 600 meters for example.

For neutralizing the stabilized feed-back reaction my invention as disclosed in the aforesaid copending application comprises the further provision of a resistance R in the output circuit o"of a magnitude such that it functions for producing a feed-forward of energy from the input circuit '11 to the output circuit 0' to compensate or neutralize the feed-back of energy taking place from the output circuit 0 to the input, circuit 71. In the present embodiment of the invention, this resistance is preferably about 2000 ohms, its value being dependent upon the residual capacities and especially the plate-ground capaclty, the value of this resistance increasing as the plate-ground capacity is reduced. This resistance maybe a fixed resistance and the same neutralizes the feed-back reaction substantially over the whole wave length range of the system. The resistance R is preferably inductance and capacity free, and the coupling inductance L is preferably made substantially resistancefree. Preferably also the input circuit 2' of the second tube is provided with a leak resistance Z which may be from to m'egohms, and the output circuit 0' is as usual provided with the B battery source of energy generally designated as B.

As heretofore stated, I have found-that in the operation of a system of the character thus far described, a disturbing reaction may take place. on any tunable input circui't, Such for example as the input circuit due to the tuning of the succeeding tuned circuit, such as the second output circuit 0 1 which is separated from the former by the untuned stage of amplification embodied in the coupled circuits 0z' this disturbing reaction being a distant stage feed-back re-' action; and as heretofore pointed out, the principal object of my present invention resides in the provision of means for compensating or neutralizing this distant stage source of feed-back reaction. I have found experimentally that when the coupling condenser K is connected with the output resistance R at a' point an at or near the plate of the first tube, the reaction upon the first tuned circuit i due to tuning the second circuit 0 to resonance with the desired signal wave serves to increase the apparent resistance of the first input circuit and so cause a loss of its selectivity. This I believe to be due in large part to the fact that'the tuning of the second output circuit 0 to resonance when such connection is made causes an increase in the input capacity of the second tube which is efi'ective from plate to ground of the first tube; and that such an increase of capacity increases the feed-forward action of the first output circuit. I have further empirically determined that the connection of the coupling condenser K to a pointy on the resistance R at or near the junction point of the resistance R and the coupling inductance L causes a change in the feed back reaction due tothe tuning of the output circuit 0 whereby the resistance of the tuned circuit 2" is apparently diminished, resulting in an increase of selectivity of this circuit and in some cases of self-sustained oscillations therein. This I believe in turn to be due in large part to the fact that the tuning of the second circuit 0 to resonance when such latter connection is made, in cansing the aforesaid increase of input capacity of the second tube produces in-efi'ect an increased capacity across the coil in the first output circuit; and that such an increase of capacity increases the feed-back reaction across the first tube. I have furthermore experimentally determined that the connection of the coupling condenser K to a point on the resistance R between the points a: and :2 such as to a point 2 thereof, results in the substantial disappearance of this disturbing distant stage. feed-back reaction. This disappearance of the disturbing distantstage feed-back reaction therefore is, as I believe, due in large measure to the fact that when the intermediate tap is made the feed-forward action due to the increased capacity across part of the resistance to ground just neutralizes .the increased feedback reaction due to the increased capacity across the said coil in the output circuit.

Therefore to neutralize the distant stage reaction, the condenser K is connectedto the resistance R so that a portion of said resistance is included in the input circuit results the connection point should be such that the resistance common to the outpu circuit 0 and input circuit i should be from one-fourth to one-half of the whole resistance R; and I have furthermore determined that this optimum connecting point for substantially no, reaction is constant through the whole tuning range of the tuning condensers C and C". This constancy of position renders it possible to have all of the elements connected with the non-tunable output circuit fixed and non-adjustable over the whole tuning range and over a moderate range of plate and filament voltage variation such as might normally occur through extended commercial use; and I have illustrated the invention by showing the connection at the point 2 of the resistance a fixed and non-adjustable one.

For securing the desired balance in the system for neutralizing the distant stage feed-back reactions, I employ the following method: The resonant voltage in the first tunable circuit i is first observed due to impressing on that circuit a constant alternating E. M. F. (the signal). This voltage will change when the second tunable circuit is varied through resonance, indicating the presence of assisting or damping reactions. For neutralizing these reactions over the whole Wave length range, the input circuit 2' is tapped onto the resistance R and the coupling tap a is adjusted along the resistance R as indicated by the arrows in the drawing until the resonant voltage in the input circuit 2" is the same or remains constant when the second tunable circuit 0 is either entirely ofi' resonance or exactly in resonance. When constancy of resonant voltage is effected, the coupling tap is fixed.

As heretofore stated, theexact-value of the plate resistance for neutralizing the adjacent stage feed-back depends upon the residual capacities and especially the plateground capacity, the value of this neutralizing resistanceincreasing as the plate-ground capacity is reduced. pling tap z is adjusted along the resistance R to balance the distant stage feed-hack, the plate-ground capacity effective in the plate circuit is varied. This will be appreciated when it is seen that the capacity in space of the coupling condenser K together with the connecting wires and the grid filament capacity of the succeeding tube is in shunt to a variable portion of the resistance R. Therefore adjustment of the tap serves to change the value of R and consequently slightly unhalances the exact adjacent stage Now when the couneutralization. For example, by moving the tap 2 towards the plate or point x, the

plate-ground capacity effective on the resistance It is increased and hence the adjacent stage neutralization is slightly unbalanced.

To secure an exact balance for both the distant and adjacent stage feed-back reactions, I have found that the value of the resistance R may be re-adiusted or modified after the first adjustment of the tap is made and an effective exact balance may be obtained by a process of successive approximation. Therefore after the first tap a'djustment is made the value of the resistance R is reduced and the unbalance of the adjacent stage feed-back is thereby eliminated. The exact balance is obtainable by a process of successive approximation and only a few trials are necessary, since the change in the total resistance It is small as the tap point is aried.

By means of the cascaded tube system thus described and as shdwn in Fig. 2 of the drawings wherein the adjacent stage feed-back re;ction from the untuned to the tuned stage is stabilized and neutralized and wherein the distant stage feed-back reaction from the second tunable stage to the .first tunable stage over the intermediate untuned stage is fully compensated for, I am enabled to successfully cascade a large number of radio frequency stages of amplification, such for example as six stages of amplification; and such a system is diagrammatically depicted in Fig. 1 of the drawings.

Referring now to Fig. 1 of the drawings, I show a radio frequency receiving system having six stages of radio frequency amplification designated 1 R. F. to 6 RF. followed by a stage of detection designated Det. connected to an antenna Ant. or other suitable receiving means. In this receiving svstem the coupled arrangement shown in Fig. 2 of the drawings comprises the first two stages 1 R. F. and 2 R. F.. the said coupled arrangement being duplicated as stages 3 R. F. and 4 R. F., the components of these stages being designated by reference characters corresponding to those shown in Fig. 2 of the drawings. The fifth stage of radio frequency 5 R. F. comprises a tuned input circuit 1F having the tuning condenser C and the output circuit 0 which includes. the coupling impedance L similar to the coupling impedance L and a feedt'orward resistance R having a magnitude preferably equal to about 1500 ohms, the input circuit 71 of the next succeeding stage 6 R. F. having a condenser K substantially equal in magnitude to the condenser K associated with the second stage 2 It. F., the said condenser being connected'to. the end of the resistance R at the plate 3) of the fifth radio frequency tube. In this stage the connection is not made to an intermediate point of the resistance because the next coupling stage as will be described presently is not tunable.

The last radio frequency stage 6 B. F. is coupled to the detector tube Det. by means of a non-tunable transformer T having the primary P and secondary S, the output detector circuit 0 being connected to the telephones Tel. or being cascaded to one or two stages of audio frequency amplification units as desired.

The principle of operation of my improved radio frequency system and the many advantages thereof will, it is thought, -be fully apparent from the above detailed description of the construction and mode of use thereof. It will further be apparent that while I have shown and described my invention in the preferred form, that many changes and modifications may be made in the structure disclosed without departing from the spirit of the invention, defined in the following claims.

I claim:

1. An amplifying system comprising a pair of electron discharge tubes, each having input and output circuits capa'citively coupled through the electrostatic coupling of the tube elements, means for tuning the input circuit of the first tube, means for tuning the output circuit of the second tube, the output'circuit of the first tube being connected by non-tunable means to the input circuit of the second tube, said non-tunable means comprising a coupling inductance and a resistance in the output circuit of the first tube for compensating for the feed-back reaction due to said coupling inductance, a portion of said resistance being included in the input circuit of the second tube for substantially neutralizing the distant stage feed-back reaction of the tuned output circuit of the second tube on the tuned input circuit of the first tube.

2. An amplifying system comprising a pair of electron discharge tubes, each having input and output circuits capacitively coupled through the electrostatic coupling of the tube elements, means for tuning the input circuit of the first tube through a predetermined frequency range, means for tuning the output circuit of the second tube through the same predetermined frequency range, the output circuit of the first tube be ing connected by non-tunable means to the input circuit of the second tube, said nontunably connected circuits having a natural frequency greater than the highest frequencg of said predetermined frequency range, sai

non-tunable means comprising a coupling inductance and aresistance in the output cir cuit of the first tube for compensating for the feed-back reaction due to said coupling inductance, a portion of said resistance being included in the input circuit of the secthe tube elements, means ond tube; for substantially neutralizing the distant stage feed-back reaction of the tuned output circuit of the second tube on the timed input circuit of the first tube.

3. An amplifying system comprising a pair of electron discharge tubes, each having input and output clrcuits capacltively coupled through the electrostatic coupling of the tube elements, means for tuning the input circuit of the first tube through a, predetermined frequency range, means for tuning the output circuit of the second tube through the same predetermined frequency range, the output circuit of the first tube being connected by non-tunable,means to the input circuit of the second tube, means for stabilizing the reactions of said non-tunably conne'cted circuits on the tuned input circuit whereby an energy feed-back reaction from the output to the input circuit of the first tube is produced over the whole frequency range, said non-tunable means comprising a coupling inductance and a resistance in the output circuit of the first tube for compensating for the feed-back reaction due to said coupling inductance, a portion of said resistance be1ng included in the input circuit of the second tube for substantially neutralizing the distant stage feed-back reaction of the tuned output circuit of the second tube .on the tuned input circuit of the first-tube.

4. An amplifying system comprising a pair of electron discharge tubes, each having input and output circuits capacitively coupled through the electrostatic coupling of for tuning the input circuit of the first-tube, means for tuning the output circuit of the second tube, the output circuit of the first tube being coupled by non-tunable means to the input circuit of the second tube, said non-tunable means comprising a coupling inductance common to the coupled circuits and a resistance of the order of 2000 ohms in the output circuit of the first tube for compensating for the feedback reaction due to said coupling inductance, the input circuit of the second tube befix'edly connected to a point intermediate the ends of said resistance for substantially neutralizing the distant stage feed-back reaction of the tuned output circuit of the secv ond tube on the tuned input circuit of the first tube.

5. An amplifying system comprising a pair of electron discharge tubes, each having input and output. circuits capacitively coupled through the electrostatic coupling of the tube elements, means for tuning the input circuit of the first tube through a pre determined frequency range, the output circuit of the first tube being coupled by nontunable means to the input circuit of the second tube, said non-tunable coupling means comprising an inductance common to the coupled circuits, means for producing an energy 'feed-back reaction from the non-tum able coupled circuits to the input circuit of the first fr uency range and means for neutralizing said feed-back reaction.

' 6. An amplifying system comprising a. pair of electron discharge tubes, .each having input and output circuits'capacitively coupled through the electrostatic coupling of the tube elements, means for tuning the input circuit of the first tube through a predetermined frequency range, the output circuit of the first tube being coupled by nontunable means to the input circuit of the second tube, said non-tunable coupling means comprising an inductance common to the coupled circuits, means for producing an energy feed-back reaction from the'non-turnable coupled circuits .to the input circuit of the first tube for the whole predetermined frequency range and a resistance in the out; put circuit .of the first tube for neutralizing said feed-back reaction. 7. An amplifying system comprising a pair of electron d'echarge tubes, each having input and output circuits capacitively coupled through the electrostatic coupling of the tube elements, means for tuning the input circuit of the first tube through a pre determined frequency range, the output circuit of the first tube being coupled by nontunable means to the input circuit of the second tube, said non-tunable coupled circuits having a natural frequency greater than the highest frequency of said predetermined frequency range, said non-tunable coupling means comprising an inductance common to the coupled circuits, and a resistance in the output circuit of the tion of which is included in the input circuit of the second tube.

8. In an amplifying system in which a pair of electron discharge tubes are coupled in cascade by non-tunable means consisting of a coupling inductance and a resistance i which the input circuit of the first tube and the output circuit of the second tube are tun,-

first tube at leasta por tube for the whole predetermined able, the method of securing a balance in there system for neutralizing the feed-back reaction of the second tunable circuit on the first tunable circuit which consists in tappin the input circuit of the'second tube onto sai resistance and in adjusting the tap until the resonant voltage of the first tunable circuit is constant as the second tunable circuit is moved into and out of resonance.

9. In an amplifying system in which a pair of electron discharge tubes are coupled in cascade by non-tunable means consisting of a coupling inductance common to the coupled circuits and a resistance in the output circuit of the first tube and in which the input circuit of the first tube and the output circuit of the second tube are tunable, the

1 1.0 the output circuit of the first tube and in method of securing a balance in the system for neutralizing the feed-back reaction of the second tunable circuit on the first tunable circuit which consists in end of the input circuit of the second tube onto said resistance and in adjusting the tap until the resonant voltage ofthe first tunable circuit is constant as the second tunable circuit is moved into and out of resonance.

10. In an amplifying system in which a pair of electron-discharge tubes are coupled in cascade by non-tunable means consisting of a coupling inductance and a resistance in the output clrcuit of the first tube and in which the input circuit of the first tube and the output circuit of the second tube are tunable, the method of securing a balance in the system for neutralizing the adjacent stage feed-back tapping the grid until the'resonant voltage of the first reaction due to said coupling inductance and the distant stage feed-back reaction due to the efiect of the second tunable circuit on the first tunable circuit, which consists in tapping the input circuit of the second tube onto said resistance, in first adjusting the tap tunable circuit is constant as the second tunable circuit is moved into and out of'resonance and in thereafter readjusting the value-of said resistance to compensate for the imbalance of the adjacent stage feed-back due to the tap adjustment.

Signed at New New York and State of New York, this 1st day of March, All 1926.

" LESTER L. JONES.

York city in the county of i 

